In recent years, the need for a surface light-emitting element with low power-consumption and small volume has been growing, and an organic electroluminescent element (hereinafter referred to as an organic EL element) as one of such the surface light-emitting element has been attracting attention.
The organic EL element is made so that it injects electrons and holes from an electron injecting electrode and a hole injecting electrode respectively into a light emitting layer, recombines in the light emitting layer the electrons and holes injected in such a way, raises an organic material to an excited state, and then the organic material emits light when the material returns from the excited state to the ground state, and has a feature that the element can be driven with a low voltage. Further, it is expected that the element will be developed as a thin and flexible lighting application by taking advantage of the surface light emission characteristic.
Hereinafter, the light emitting body structured by using the above organic EL element is referred to as an organic EL panel.
As a failure of the organic EL element, there has been known a failure which is originated from production of the organic EL element and can not be recognized in an initial state but becomes obvious with lighting time of the organic EL panel, and the light emission suddenly stops. The failure (a defect) incurs a sudden stop of the light emission of the organic EL panel, and, in particular, when the organic EL panel is used for lighting, the failure leads to a sudden stop of the light emission, whereby it has become a problem such as an adverse effect on safety environment.
Hereinafter, the sudden stop of the light emission of the organic EL panel is also referred to as a sudden death of the organic EL panel.
On the above problem, there has been disclosed an inspection device in which a reverse pulse voltage having a predetermined voltage and a predetermined pulse width, which becomes a reverse bias condition to an organic EL element, is applied to the organic EL element, and then, an image of the organic EL element, which is in a state that the above reverse pulse voltage is applied, is taken in a light shielding state by an image taking means, and subsequently the number of light emitting points exhibiting higher brightness than the predetermined one is counted using an image inspection means, whereby the organic EL element is judged to be superior or inferior (refer, for example, to Patent Document 1).